On 9/11, a whole generation was traumatized and a cohort of heroes was created who responded to a call to help in the search, rescue, and cleanup efforts in Manhattan. While we understand the current troubles that such individuals face, we have very little knowledge about what they can expect as they age. Yet, these first responders now average age 52 and may already be experiencing rapid aging as 24% report having poor memories and 14% screen positive for mild cognitive impairment, which precedes dementia in over 80% of cases. Responders are not alone in experiencing dementia: as many as 5 million Americans currently live with Dementia, while over 15 million are charged with caretaking responsibilities for friends and family members who are cognitively impaired. One theory that has recently arisen is that severe traumatic experiences, leading to chronic forms of post-traumatic stress, have long-term implications for brain aging. In particular, it is possible tat such traumas severely decrease the ability for the brain to resist injury and to remain healthy. However, to date research has been hampered by small sample sizes and limited opportunity for life course analysis. Preliminary analyses show substantial support for the view that PTSD impacts cognition at baseline and provide support for the view that PTSD may be determined by similar factors influencing resilience as is cognitive aging. Furthermore, preliminary evidence is also suggestive that PTSD is strongly associated with poorer cognition, even in this highly educated and generally employed cohort. The study of aging demands an integrative life course developmental framework, involving interdisciplinary collaborations and advanced methodological approaches for understanding what modifies healthy aging. Taking this into account, this project has four specific aims. First, it will examine the role of individual and socal characteristics in influencing cognitive reserve. Second, it will evaluate the relationship between PTSD and cognitive aging in the WTC first-responder cohort. Third it will examine the biological mechanisms linking PTSD to cognitive aging. Finally, it will examine the social and behavioral mechanisms linking PTSD to cognitive aging.